奈良県月瀬村五月川における藻類と水棲昆虫の生態学的研究

抄録

The algae and the aquatic insects in the riffle and pool of Satsuki-gawa, Tsukigase-mura of Nara Prefecture were ecologically studied from the first to third of August in 1956. (1) As a result of comparing and discussing the algal communities of 4 points in a riffle (Fig. 1 )where current velocities were different, it was found that, as they changed from a point of large current velocity to that of small one, the structures of the communities changed as follows. Cyanophyceae community→Cyanophyceae and Diatomaceae community→Chlorophyceae and Diatomaceae community (Table 1,2). The quadrate of 50cm×50cm was set in the riffle and algae and aquatic insects were quantitatively collected. As the result, the dry weight of the sample excluding the aquatic insects was 10.93g, the ash and mineral substance weighed 6.58g and the ignition loss, 4.35g. The constitution of the algal community in this quadrate had a strong resemblance to that of the point C where the current velocity was almost equal(Table 1,2). (2) At a pool of about two metres deep(Fig. 2)an experiment was made to find the relation between the light intensity and the production by the photosynthesis of algae according to the difference of the depth. At the same time, the algal communities at some points of different depth were studied. The result is as follows. In the pool above mentioned the production by assimilation reduced considerably as the depth increased ; but the constitution of the benthic algal community in different depth remained almost the same. Consequently, the light as the environmental factor is considered not to have enough influence to change the components of algal community in this degree of the difference of depth(Tables 1,2,3). Besides, the structures of algal communities of the points E, F, G of the pool(Table 2)resembled to that of the point A of riffle where the current velocity was very small. (3) The floating matters were collected quantitatively by a plankton net in the riffles and pools, and the dry weight of the sample, the weight of ignition residue and that of ignition loss were measured. The ignition residue represents almost the abioseston, the ignition loss represents almost the bioseston.(We wish to name the matter carried by the current potamoseston). Also, the percentage constitution of each species of algae in the flowing matter samples was examined (H, I, J in Table 2). Ecological meanings of the flowing matters were discussed from the results of the above studies. (4) Rich insect fauna (Table 5) was found in the riffle, the standing crop being caluculated as 40 gr/m^2. On the contrary the insect community in the pool was very poor, its standing crop was only 0.081 gr/m^2.